1. Field of the Invention
The present invention relates to an angular velocity sensor suitable for use in detecting an angular velocity.
2. Description of the Related Art
As a first example of a known angular velocity sensor, Japanese Unexamined Patent Application Publication No. 5-312576 discloses an angular velocity sensor which includes a substrate, a mass member which is retained by retaining beams attached to the substrate such that the mass member can move in two perpendicular directions, a vibration generator for vibrating the mass member in a vibration direction which is one of the two perpendicular directions that is parallel to the substrate, and an angular velocity detector which detects an angular velocity on the basis of a displacement of the mass member in a detection direction which is perpendicular to the vibration direction.
In such an angular velocity sensor, among X and Y axes which are parallel to the substrate and a Z axis which is perpendicular to the substrate, the mass member is vibrated in, for example, the X-axis direction with a predetermined amplitude. When an angular velocity about the Z axis is applied to the mass member while it is vibrating in the above-described manner, a Coriolis force is applied to the mass member in the Y-axis direction. Accordingly, the mass member moves in the Y-axis direction, and the angular velocity detector detects the displacement of the mass member on the basis of a capacitance change and outputs a detection signal corresponding to the angular velocity.
In this case, the mass member is retained by the retaining beams provided on the substrate in such a manner that the mass member can move (vibrate) in the X-axis direction. One end of each retaining beam is fixed to the substrate, and the other end is connected to the mass member. While the angular velocity sensor is activated, the retaining beams are deflected such that the mass member vibrates in the X-axis direction.
As a second example of a known angular velocity sensor, Japanese Unexamined Patent Application Publication No. 7-218268 discloses an angular velocity sensor which is called a tuning fork gyroscope, wherein a pair of mass members are arranged above a substrate and are vibrated in opposite phases, so that vibrations of the mass members transmitted to the substrate via retaining beams cancel each other.
In such a case, the retaining beams have a complex shape including a plurality of bent portions in order to retain each of the mass members at a predetermined position. One end of each retaining beam is split into two portions which are connected to the two mass members.
In the above-described first example, the mass member is connected to the substrate by the retaining beams. Therefore, when the mass member vibrates above the substrate, the vibration is easily transmitted to the substrate via the retaining beams.
Accordingly, when the angular velocity sensor is activated, vibration energy is transmitted to the substrate and the amplitude and the vibration velocity of the mass member are reduced. Thus, the Coriolis force due to the angular velocity is also reduced and the detection sensitivity decreases. In addition, when the vibration is transmitted to the substrate, the mass member may vibrate in the detection direction due to the vibration of the substrate even when no angular velocity is applied. Accordingly, the detected angular velocity often includes an error, and reliability of the angular velocity sensor decreases.
In the above-described second example, the mass members are vibrated in opposite phases so that the vibrations of the mass members transmitted to the substrate cancel each other. However, the mass members are retained by the retaining beams having a complex shape with bent portions, and it is difficult to manufacture the retaining beams having the same size, shape, deflection characteristics, etc.
Accordingly, in the second example, the mass members may vibrate in different manners due to the difference in size between the retaining beams, processing errors, etc. In such a case, the vibrations of the mass members transmitted to the substrate via the retaining beams cannot reliably cancel each other.
On the other hand, when an acceleration is applied to the angular velocity sensor in the Y-axis direction due to an external force, such as an impact force, while the angular velocity sensor is activated, the mass members may move in the Y-axis direction not only due to the Coriolis force caused by the angular velocity but also due to an inertial force caused by the acceleration. In such a case, although the detected displacement includes both an angular-velocity component and an acceleration component, the angular velocity is determined on the basis of the detected displacement.
Therefore, even a small impact applied to the angular velocity sensor causes an error corresponding to the acceleration component in the angular-velocity detection signal and decreases the accuracy in detecting angular velocity. Accordingly, it is difficult to ensure the reliability of the sensor.
If the acceleration applied to the angular velocity sensor includes a frequency component that is close to the vibration frequency of the mass members, the error due to the acceleration component cannot be reliably removed even by signal processing, such as synchronous detection, in which the detection signal is synchronously rectified at a period corresponding to the vibration frequency and integrated to separate the angular-velocity component.
In order to overcome the problems described above, preferred embodiments of the present invention provide a high-sensitivity, high-accuracy, and high-reliability angular velocity sensor which prevents vibrations of mass members from being transmitted to a substrate via retaining beams and in which the mass members vibrate in a stable vibrational state.
According to a preferred embodiment of the present invention, an angular velocity sensor includes a substrate, four mass members which face the substrate with a gap between each mass member and the substrate, the mass members being arranged along a Y-axis direction when X, Y, and Z axes that are perpendicular to each other are defined, retaining beams which connect the mass members such that the mass members can move in the X-axis direction, a fixing member disposed between the substrate and the retaining beams to fix the retaining beams to the substrate, a vibration generator which vibrates at least one of the mass members in the X-axis direction so that the adjacent mass members vibrate in opposite phases, and an angular velocity detector which detects an angular velocity on the basis of displacements of two of the four mass members which are disposed symmetrically about the central position in the Y-axis direction when the two mass members disposed symmetrically about the central position move in at least one of the Y and Z-axis directions by the angular velocity.
Accordingly, the four mass members can be connected to each other by the retaining beams along the Y-axis direction, which is perpendicular to the vibrating direction (X-axis direction). By vibrating at least one of the mass members by the vibration generator, the four mass members can be vibrated such that two adjacent mass members are in opposite phases. The retaining beams which connect the mass members are provided with vibration nodes, which are maintained at predetermined positions when the retaining beams vibrate along with the mass members.
Since the two mass members which are disposed symmetrically about the central position (at the central region or at the outside in the Y-axis direction) vibrate in opposite phases, these two mass members move in the opposite directions due to a Coriolis force when the angular velocity is applied, and move in the same direction due to an inertial force when an acceleration is applied. Therefore, the displacements thereof in the same direction (acceleration components) can be canceled by calculating the difference between the displacements of these two mass members, and the angular velocity can be detected separately from the acceleration.
In addition, since the four mass members are arranged along the Y-axis direction, the overall center of gravity of the four mass members can be maintained at an approximately certain position while the mass members vibrate. Accordingly, the mass members can vibrate in a stable vibrational state and the vibrations thereof can be prevented from being transmitted to the substrate. The two mass members disposed symmetrically about the central position in the Y-axis direction are preferably arranged such that the shapes thereof are symmetrical with respect to the overall center of gravity of the four mass members. In such a case, the resonance frequencies and the amounts of deformation due to temperature variation of the two mass members disposed at the central region are approximately the same. Therefore, the two mass members disposed at the central region move by approximately the same distance when an acceleration is applied. As a result, the acceleration components can be reliably eliminated by calculating the difference between the displacements of the two mass members disposed at the central region and the detection accuracy of the angular velocity can be increased.
As described above, according to a preferred embodiment of the present invention, the four mass members are connected by the retaining beams and are vibrated in the X-axis direction such that two adjacent mass members are in opposite phases. The four mass members are preferably arranged such that the shapes thereof are symmetrical with respect to the overall center of gravity in the Y-axis direction. In such a case, the four mass members can vibrate in a stable vibrational state such that two adjacent mass members are in opposite phases while the overall center of gravity is maintained at an approximately constant position. Accordingly, the mass members can vibrate with a good balance and reaction forces generated while the mass members vibrate can reliably cancel each other. Therefore, the vibrations can be more reliably prevented from being transmitted to the substrate. In addition, even when there are small dimensional errors or processing errors, differences in resonance frequencies, etc., between the mass members due to such errors can be compensated for by their symmetrical shapes. Accordingly, when the acceleration is applied due to external vibration, impact, etc., the mass members which vibrate in opposite phases move by approximately the same distance, and the displacements due to the acceleration can be reliably canceled by the angular velocity detector. Therefore, the angular velocity can be accurately detected separately from the acceleration, and the performance and reliability of the sensor can be improved.
In the angular velocity sensor of preferred embodiments of the present invention, preferably, the angular velocity detector detects an angular velocity on the basis of displacements of two of the four mass members which are disposed at the central region in the Y-axis direction when the two mass members disposed at the central region move in at least one of the Y and Z-axis directions by the angular velocity.
In the angular velocity sensor of preferred embodiments of the present invention, preferably, the retaining beams are fixed to the substrate by the fixing member at portions corresponding to nodes of the retaining beams when the mass members vibrate such that two adjacent mass members are in opposite phases.
Since the fixing member fixes the retaining beams to the substrate at positions corresponding to the nodes of the retaining beams when the mass members vibrate, the vibrations of the mass members can be reliably prevented from being transmitted to the substrate via the retaining beams, and the detection accuracy of the angular velocity sensor can be further increased.
In addition, according to preferred embodiments of the present invention, preferably, the four mass members are arranged linearly in the Y-axis direction and the retaining beams extend linearly in the Y-axis direction and connect the mass members.
Accordingly, when, for example, one of the mass members is vibrated in the X-axis direction, the vibration thereof is efficiently transmitted to the other mass members via the retaining beams. Thus, the mass members can be vibrated such that two adjacent mass members are in opposite phases with a simple structure. In addition, the vibrational state (vibration mode) of each mass member can be determined by the deflection of the linear retaining beams. Accordingly, even when there are small processing errors in the mass members, the two mass members disposed at the central region can be vibrated at approximately the same amplitude, and stable detection sensitivity can be obtained.
In addition, according to preferred embodiments of the present invention, preferably, the four mass members include a pair of mass members disposed at the central region in the Y-axis direction and a pair of mass members disposed at positions outside the mass members disposed at the central region, and a first pair selected from the two pairs of mass members moves in the Y-axis direction in accordance with an angular velocity about the Z axis and a second pair of the two pairs of mass members moves in the Z-axis direction in accordance with an angular velocity about the Y axis. In addition, the angular velocity detector includes a first angular velocity detector element for detecting the angular velocity about the Z axis on the basis of displacements of the first pair of mass members and a second angular velocity detector element for detecting the angular velocity about Y axis on the basis of displacements of the second pair of mass members.
Accordingly, the angular velocity about the Z axis can be detected, for example, by the mass members disposed at the central region while the angular velocity about the Y axis is detected by the mass members disposed at the outside. Alternatively, the angular velocity about the Y axis can be detected by the mass members disposed at the central region while the angular velocity about the Z axis is detected by the mass members disposed at the outside. Thus, the angular velocity sensor functions as a two-axis angular velocity sensor which detects angular velocities about two axes individually. In addition, the overall size of the two-axis angular velocity sensor can be reduced, and signal processing circuits and electric wiring for the sensor can be made simpler.
In addition, according to preferred embodiments of the present invention, preferably, each of the two mass members disposed at the central region includes a central frame having a frame shape and a horizontal vibrator which is disposed inside the central frame such that the horizontal vibrator can vibrate in the Y-axis direction along the substrate, and the angular velocity detector detects an angular velocity about the Z axis on the basis of displacements of the horizontal vibrators in the Y-axis direction.
Accordingly, while the angular velocity is not applied, the vibrator only vibrates in the X-axis direction in the central frame even when the retaining beams are deflected. Thus, the deflection of the retaining beams can be prevented from being transmitted to the vibrator as a displacement in the Y-axis direction, and the detection accuracy of the angular velocity about the Z axis can be further increased.
In addition, according to preferred embodiments of the present invention, preferably, the angular velocity detector includes first and second displacement detectors for detecting a displacement in the Y-axis direction of the horizontal vibrator of one of the two mass members disposed at the central region, and third and fourth displacement detectors for detecting a displacement in the Y-axis direction of the horizontal vibrator of the other one of the two mass members disposed at the central region.
Since the two mass members disposed at the central region in the Y-axis direction vibrate in opposite phases, they move in the opposite directions due to the Coriolis force when an angular velocity about the Z axis is applied, and move in the same direction due to the inertial force when an acceleration is applied in the Y-axis direction. Accordingly, by adding, or obtaining the difference between the displacement of the horizontal vibrator detected by the first and second displacement detectors and the displacement of the other horizontal vibrator detected by the third and fourth displacement detectors, the displacements in the same direction (acceleration components) can be canceled and eliminated, so that the angular velocity can be detected separately from the acceleration and variations in sensitivities due to thermal distortion can be canceled.
In addition, according to preferred embodiments of the present invention, preferably, the first and second displacement detectors include first and second fixed detection electrodes and first and second movable detection electrodes, respectively, the first and second fixed electrodes being provided on the substrate and the first and second movable electrodes being provided on the corresponding horizontal vibrator and facing the first and second fixed detection electrodes, respectively, with gaps therebetween in the Y-axis direction. When the angular velocity about the Z axis is applied, the movable detection electrode moves toward the fixed detection electrode in one of the first and second displacement detectors and the movable detection electrode moves away from the movable detection electrode in the other one of the first and second displacement detectors move away from each other. In addition, preferably, the third and fourth displacement detectors include third and fourth fixed detection electrodes and third and fourth movable detection electrodes, respectively, the third and fourth fixed electrodes being provided on the substrate and the third and fourth movable electrodes being provided on the corresponding horizontal vibrator and facing the third and fourth fixed detection electrodes, respectively, with gaps therebetween in the Y-axis direction. When the angular velocity about the Z axis is applied, the movable detection electrode moves toward the fixed detection electrode in one of the third and fourth displacement detectors and the movable detection electrode moves away from the movable detection electrode in the other one of the third and fourth displacement detectors move away from each other.
Accordingly, when an angular velocity about the Z axis is applied, the capacitance between the fixed detection electrode and the movable detection electrode increases, for example, in the first and the third displacement detectors while the capacitance between the fixed detection electrode and the movable detection electrode decreases in the second and the fourth displacement detectors. In such a case, when an acceleration is applied in the Y-axis direction, the capacitance between the fixed detection electrode and the movable detection electrode increases, for example, in the first and the fourth displacement detectors while the capacitance between the fixed detection electrode and the movable detection electrode decreases in the second and the third displacement detectors.
Accordingly, the acceleration components can be canceled and eliminated by adding the capacitances in the first and the third displacement detectors and adding the capacitances in the second and the fourth displacement detectors, so that the angular velocity can be detected separately from the acceleration. In addition, since the sum of the capacitances in the first and the third displacement detectors and the sum of the capacitances in the second and the fourth displacement detectors vary (increase and decrease) in the opposite phases, a signal corresponding to the angular velocity can be magnified by obtaining the difference between these two sums.
In addition, according to preferred embodiments of the present invention, preferably, the angular velocity detector includes a first displacement detector for detecting a displacement in the Y-axis direction of the horizontal vibrator of one of the two mass members disposed at the central region, and a second displacement detector for detecting a displacement in the Y-axis direction of the horizontal vibrator of the other one of the two mass members disposed at the central region. The first displacement detector includes a first fixed detection electrode which is provided on the substrate and a first movable detection electrode which is provided on the corresponding horizontal vibrator and faces the first fixed detection electrode with a gap therebetween in the Y-axis direction, and the second displacement detector includes a second fixed detection electrode which is provided on the substrate and a second movable detection electrode which is provided on the corresponding horizontal vibrator and faces the second fixed detection electrode with a gap therebetween in the Y-axis direction.
Since the two mass members disposed at the central region in the Y-axis direction vibrate in opposite phases, they move in the opposite directions when an angular velocity about the Z axis is applied. When each of the two displacement detectors includes a fixed detection electrode and a movable detection electrode, the two displacement detectors can be set such that the capacitances between the fixed detection electrodes and the movable detection electrodes of the two displacement detectors increase or decrease in the same phase or in the opposite phases. Accordingly, the angular velocity about the Z axis can be detected by adding or obtaining the differences between the capacitances in the two displacement detectors.
When the angular velocity about the Z axis is applied, the first and second movable detection electrodes may move toward or away from the first and second fixed detection electrodes, respectively, in the first and second displacement detectors at the same time.
In this case, when an acceleration is applied in the Y-axis direction, the two horizontal vibrators move in the same direction. In addition, the capacitance in one of the two displacement detectors increases and the capacitance in the other one of the two displacement detectors decreases. Accordingly, the capacitance changes due to the acceleration can be canceled and eliminated by adding the capacitances in the two displacement detectors, so that the angular velocity can be detected separately from the acceleration.
Alternatively, when the angular velocity about the Z axis is applied, the movable detection electrode may move toward the fixed detection electrode in one of the first and second displacement detectors while the movable detection electrode moves away from the fixed detection electrode in the other one of the first and second displacement detectors.
In this case, when an acceleration is applied in the Y-axis direction, the two horizontal vibrators move in the same direction and the capacitances in the two displacement detectors increase and decrease together. Accordingly, the capacitance changes due to the acceleration can be canceled and eliminated by obtaining the difference between the capacitances in the two displacement detectors, so that the angular velocity can be detected separately from the acceleration and variations in sensitivities due to thermal distortion can be canceled.
In addition, according to preferred embodiments of the present invention, preferably, each of two of the four mass members which are disposed at the outside in the Y-axis direction includes a central frame having a frame shaped configuration and a vertical vibrator which is disposed inside the central frame such that the vertical vibrator can vibrate in the Z-axis direction, which is perpendicular to the substrate, and the angular velocity detector detects an angular velocity about the Y axis on the basis of displacements of the vertical vibrators in the Z-axis direction.
Accordingly, the mass members disposed at the outside can move toward/away from the substrate in the Z-axis direction in accordance with the angular velocity about the Y axis while they vibrate in the X-axis direction, and the angular velocity about the Y axis can be detected on the basis of the displacements of these mass members.
In addition, the angular velocity about the Z axis can be detected by the mass members disposed at the central region while the angular velocity about the Y axis is detected by the mass members disposed at the outside. Thus, the angular velocity sensor functions as a two-axis angular velocity sensor which detects angular velocities about two axes individually.
In addition, according to preferred embodiments of the present invention, preferably, the fixing member includes arm portions which are deflected in the Y-axis direction while retaining the mass members when an acceleration is applied to the mass members in the Y-axis direction.
Accordingly, the four mass members can be retained by arm portions having elasticity (spring characteristics) in the Y-axis direction. Therefore, when, for example, the mass members move (vibrate) in the Y-axis direction due to disturbance such as acceleration, the mass members vibrate while they are elastically connected to each other by the arm portions (coupled vibration), so that vibration energies of the mass members are transmitted between the mass members due to the elastic force of the arm portions. Therefore, even when the amplitudes of the mass members corresponding to a predetermined acceleration are different from each other due to dimensional errors or processing errors, the differences in vibration amplitude between the mass members can be reduced as the vibration energies are transmitted between them, and the influence of the acceleration can be reliably eliminated between the mass members.
In addition, according to preferred embodiments of the present invention, preferably, the four mass members are arranged symmetrically in the Y-axis direction with respect to the overall center of gravity of the four mass members.
Accordingly, the resonance frequencies of the two mass members disposed at the central region can be set to be approximately the same, so that these mass members move by approximately the same distance when an acceleration is applied. Therefore, the acceleration components can be eliminated by calculating the difference between the displacements of these two mass members, and only the angular velocity component can be obtained. In addition, since the overall center of gravity can be maintained at an approximately constant position when the four mass members vibrate, the four mass members can vibrate in a stable vibrational state and the vibrations thereof can be prevented from being transmitted to the substrate.
In addition, even when there are small dimensional errors or processing errors, differences in resonance frequencies, etc., between the mass members due to such errors can be compensated for by their symmetrical shapes, and the performance and reliability of the sensor can be improved.
In addition, according to preferred embodiments of the present invention, preferably, masses of two of the four mass members which are disposed at the outside in the Y-axis direction are smaller than masses of the two mass members disposed at the central region. When the four mass members vibrate, a rotational moment about the overall center of gravity of the four mass members applied to the two mass members disposed at the central region is approximately the same as a rotational moment about the overall center of gravity of the four mass members applied to the two mass members disposed at the outside.
When the mass members vibrate such that two adjacent mass members are in opposite phases, the rotational moment about the overall center of gravity applied to the mass members disposed at the central region and that applied to the mass members disposed at the outside are opposite to each other. Since the mass members disposed at the outside are farther away from the overall center of gravity than the mass members disposed at the central region, the rotational moment applied to the mass members disposed at the central region and that applied to the mass members disposed at the outside can be set to be approximately the same by setting the mass of the outer mass members smaller than the mass of the central mass members.
As a result, when the mass members are vibrated by the vibration generator, the quality factor in the resonant state can be increased and the mass members can be vibrated with a large amplitude, so that stable detection sensitivity can be obtained. In addition, since the rotational moment applied to the mass members disposed at the central region and the mass members disposed at the outside cancel each other, the rotational moments can be prevented from being transmitted to the substrate as an external force. Therefore, the detection accuracy of the angular velocity sensor can be further increased.
In addition, according to preferred embodiments of the present invention, two of the four mass members which are disposed at the central region in the Y-axis direction may be provided with a vibrational state monitor for monitoring the state of vibration generated by the vibration generator on the basis of displacements of the mass members when the mass members vibrate in the X-axis direction.
Accordingly, when the angular velocity detector detects the displacements of the two mass members disposed at the central region in the Y-axis direction, the angular velocity detector and the vibrational state monitor can be disposed near each other.
In addition, when the angular velocity detector detects the displacements of the two mass members disposed at the outside in the Y-axis direction, the angular velocity detector and the vibrational state monitor can be disposed separately from each other. Therefore, a signal corresponding to the angular velocity and a signal corresponding to the vibrational state can be obtained separately with high accuracy, and there is more freedom in designing the sensor.
In addition, according to preferred embodiments of the present invention, two of the four mass members which are disposed at the outside in the Y-axis direction may be provided with a vibrational state monitor for monitoring the state of vibration generated by the vibration generator on the basis of displacements of the mass members when the mass members vibrate in the X-axis direction.
Accordingly, when the angular velocity detector detects the displacements of the two mass members disposed at the outside in the Y-axis direction, the angular velocity detector and the vibrational state monitor can be disposed separately from each other. Therefore, a signal corresponding to the angular velocity and a signal corresponding to the vibrational state can be obtained separately with high accuracy, and there is more freedom in designing the sensor.
In addition, according to preferred embodiments of the present invention, preferably, the angular velocity sensor further includes a vibrational state monitor for monitoring the state of vibration generated by the vibration generator on the basis of displacements of the mass members when the mass members vibrate in the X-axis direction, the vibrational state monitor being disposed at a portion of one of the retaining beams which corresponds to one of nodes of the retaining beam when the mass members vibrate such that two adjacent mass members are in opposite phases.
Accordingly, a monitor electrode having a relatively small inertial mass can be rigidly attached to one of the portions corresponding to the nodes of the retaining beams where the vibrations are not easily transmitted, and be fixed to the substrate by the node and the fixing member. As a result, even when acceleration is applied to the substrate due to external vibration, impact, etc., the monitor electrode can be prevented from being accidentally moved due to the acceleration, and accurate monitor signals can be output to an external circuit, etc. In particular, the monitor electrode can be reliably prevented from being affected by the acceleration in the Z-axis direction. In addition, since the retaining beams are deflected by the amount corresponding to the amplitude of the mass members while the mass members vibrate, the vibrational state monitor can detect the vibrational state of the mass members on the basis of the amount of deflection of the retaining beams. Accordingly, the amplitudes, etc., of the mass member can be reliably feedback-controlled on the basis of the monitor signals by, for example, an external circuit. Therefore, even when there is temperature variation or when an external force is applied, the angular velocity can be detected with high accuracy, and reliability of the angular velocity sensor can be further improved.
In addition, according to preferred embodiments of the present invention, preferably, the vibrational state monitor includes a fixed monitor electrode provided on the substrate and a movable monitor electrode which is disposed on the portion of the retaining beam which corresponds to the node and which rotates around the portion of the retaining beam which corresponds to the node with respect to the fixed monitor electrode when the mass members vibrate and the retaining beams are deflected.
Accordingly, when the mass members vibrate and the retaining beams are deflected, the movable monitor electrode rotates around the node, so that the opposing area between the fixed monitor electrode and the movable monitor electrode changes in accordance with the displacement of the movable monitor electrode. Therefore, the vibrational state of the mass members can be detected on the basis of a capacitance change between the fixed monitor electrode and the movable monitor electrode. Accordingly, the vibrational state of the mass members can be accurately detected with a simple, non-contact structure.
In addition, according to preferred embodiments of the present invention, preferably, the fixed monitor electrode includes a plurality of electrode fingers having an arc shaped configuration disposed around the portion of the retaining beam which corresponds to the node, and the movable monitor electrode includes a plurality of electrode fingers having an arc shape such that the electrode fingers of the fixed monitor electrode and the electrode fingers of the movable monitor electrode oppose each other with gaps provided in the radial direction.
Accordingly, the electrode fingers of the fixed monitor electrode and those of the movable monitor electrode can have, for example, comb-like configurations arranged such that they interlock with each other, and the opposing area between the fixed monitor electrode and the movable monitor electrode can be increased. Thus, a small, high-accuracy monitor electrode unit can be obtained. In addition, since the electrode fingers of the fixed monitor electrode and those of the movable monitor electrode have an arc shape, they can move relative to each other without coming into contact with each other when the movable monitor electrode rotates around the node. In addition, the electrode fingers of the fixed electrode and those of the movable electrode oppose each other with gaps therebetween in the radial direction, and the opposing area therebetween changes proportionally to the amount of rotation (rotational angle) of the movable monitor electrode. Therefore, the capacitance between the fixed electrode monitor and the movable electrodes can be changed proportionally (linearly). Accordingly, the vibrational state of the mass members can be detected with high accuracy even when the monitor electrodes are disposed at one of the nodes of the retaining beams.
In addition, according to preferred embodiments of the present invention, preferably, the angular velocity detector includes first and second displacement detectors for detecting a displacement in the Y-axis direction of one of the two mass members disposed symmetrically about the central position in the Y-axis direction, and third and fourth displacement detectors for detecting a displacement in the Y-axis direction of the other one of the two mass members disposed symmetrically about the central position in the Y-axis direction.
Since the two mass members disposed symmetrically about the central position in the Y-axis direction vibrate in opposite phases, they move in the opposite directions when an angular velocity about the Z axis is applied and move in the same direction when an acceleration is applied in the Y-axis direction. Accordingly, by adding, or obtaining the difference between the displacement of the mass member detected by the first and second displacement detectors and the displacement of the other mass member detected by the third and fourth displacement detectors, the acceleration components included in the displacements can be canceled and eliminated, so that the angular velocity can be detected separately from the acceleration and variations in sensitivities due to thermal distortion can be canceled.
In addition, according to preferred embodiments of the present invention, preferably, the angular velocity detector includes a first displacement detector for detecting a displacement in the Y-axis direction of one of the two mass members disposed symmetrically about the central position in the Y-axis direction, and a second displacement detector for detecting a displacement in the Y-axis direction of the other one of the two mass members disposed symmetrically about the central position in the Y-axis direction.
Since the two mass members disposed symmetrically about the central position in the Y-axis direction vibrate in opposite phases, they move in the opposite directions when an angular velocity about the Z axis is applied. When each of the two displacement detectors includes a fixed detection electrode and a movable detection electrode, the two displacement detectors can be set such that the capacitances between the fixed detection electrodes and the movable detection electrodes of the two displacement detectors increase or decrease in the same phase or in the opposite phases. Accordingly, the angular velocity about the Z axis can be detected by adding or obtaining the differences between the capacitances in the two displacement detectors.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.